The present invention relates to a method and apparatus for detecting a soft foot condition of one or more machines. The term "soft foot," as used throughout this text, relates to the usage as is common among engineers, technicians etc., and is not directly related to the usage of the same term, as used in the medical or related arts. For those persons not acquainted with this term it should be explained that normally nothing is "soft" with the feet under inspection. To the contrary, the feet are quite inelastic. However, once the feet tie a machine under test to the ground in a sturdy fashion, then the geometric constraints of the feet and/or shop floor ground will cause small, but intolerable mechanical deformation or distortion of such specific machine.
It has long been recognized that setting up and installing rotating equipment and machinery requires careful layout and care in the installation. This is especially true for equipment of some size, which despite of its weight and apparent stable construction, nonetheless requires attention to maintain mechanical dimensionality within predefined tolerances, which may correspond to minute fractions of an inch or may be in the sub-millimeter range. Neglecting such prerequisites will yield slightly, but definitely distorted, machine dimensions and thus will frequently cause reduced service life. Also, suboptimum output or efficiency may result from such machines, which may be combustion engines, electric motors or generators, turbines, lathes or other machine tools, pumps, ventilators (fans), gearboxes, and many more machines of the like.
As is well known, installing and mounting such machines on uneven or rough surfaces will result in a somewhat distorted shape of their housings or enclosures, with subsequent adverse effects on the bearings for shafts, spindles or the like present in such machines. Another negative effect is in obtaining and maintaining correct alignment of the spindles of machine trains such as, for example, pumps and their driving motors. In electric motors or generators, deformation of the machine induced by inadequate mounting may have effects on the shape of the magnetic airgaps, usually reducing output power, efficiency, or both with such machinery.
There have been investigations that demonstrate the economic impact of badly mounted or aligned machine trains, in addition to the power losses. Machines in the 10 hp range may require additional maintenance cost in the range of more than U.S. $400 per horsepower per year. The importance of machines positioned correctly and aligned to stringent levels should be understood by all levels of management involved. However, considering quality terms for such machinery became more frequent just recently. An analysis of the technical aspects of the soft foot condition carried out by the present applicants discovered that contrary to common consideration, determination of the causes of a soft foot condition and advising on corrective measures are not systematically carried out. One reason for this is that there is not only one "soft foot" situation, but several classes of such, which require different corrective handling. Thus, it still may be possible for an engineer trying to eliminate a soft foot condition on a machine, to perform just the opposite and worsen conditions because of a lack of understanding or proper guidance on how to proceed to eliminate such adverse constraints on the machine.